Fuel cell system

Abstract

To provide a fuel cell system that is advantageous for maintaining an S/C value in an appropriate region even when a rotational speed of the water pump is abnormal with respect to a target rotational speed region during a power generation operation of a fuel cell. When the rotational speed of the water pump is abnormal with respect to the target rotational speed region during the power generation operation of the fuel cell, the control unit repeats a short time increase and a short time decrease of the S/C value in a reforming reaction, by alternately repeating an increase in a short time (ΔT increase, within 10 seconds) and a decrease in a short time (ΔT decrease, within 10 seconds) of the rotational speed of the water pump with respect to an abnormal rotational speed, while continuing the power generation operation of the fuel cell, thereby averaging the S/C value.

The invention claimed is: 
     
       1. A fuel cell system comprising:
 a fuel cell that is supplied with an anode gas and a cathode gas to generate electricity; 
 an evaporation unit that evaporates reforming water to generate water vapor; 
 a reforming unit that reforms a raw material gas using the water vapor generated in the evaporation unit by a reforming reaction to form the anode gas; 
 a water tank that stores the reforming water before being supplied to the evaporation unit; 
 a water supply passage that allows the water tank and the evaporation unit to communicate with each other to supply the reforming water in the water tank to the evaporation unit; 
 a water pump that supplies the reforming water in the water tank to the evaporation unit; 
 a rotational speed sensor that detects number of rotations per unit time of the water pump based on a physical quantity concerning the rotational speed of the water pump; and 
 a control unit that is programmed to input a detection signal of the rotational speed sensor and to control the water pump, 
 the control unit is programmed to presume an influence that is caused by resonance of the water pump when the rotational speed of the water pump is abnormal or is expected to be abnormal with respect to a target rotational speed region during the power generation operation of the fuel cell, and to execute an S/C value averaging control that alternately repeats an increase in a short time (ΔT increase, within 10 seconds) and a decrease in a short time (ΔT decrease, within 10 seconds) of the rotational speed of the water pump with respect to the abnormal rotational speed while continuing the power generation operation of the fuel cell, and repeats the short time increase and the short time decrease of the rotational speed of the water pump and thus a short time increase and the short time decrease of an S/C value in the reforming reaction, thereby averaging the S/C value which is directly correlated to the rotational speed of the water pump, wherein the S/C value is a molar ratio of water vapor to a carbon component contained in the raw material gas. 
 
     
     
       2. The fuel cell system according to  claim 1 , wherein the control unit is provided with a storage unit and the control unit is programmed to perform a storage control of storing and updating the abnormal rotational speed as a storage rotational speed in the storage unit each time the abnormal rotational speed occurs, and
 the control unit is programmed to alternately repeat the short time increase and the short time decrease of the rotational speed of the water pump with respect to the storage rotational speed in the S/C value averaging control. 
 
     
     
       3. The fuel cell system according to  claim 1 , wherein the control unit is provided with a storage unit and the control unit is programmed to perform a storage control of storing and updating the abnormal rotational speed as a storage rotational speed in the storage unit each time the abnormal rotational speed occurs, and
 when the rotational speed of the water pump approaches toward a storage rotational speed in the subsequent power generation operation, the control unit is programmed to alternately repeat the short time increase and the short time decrease of the rotational speed of the water pump with respect to the storage rotational speed, while suppressing or avoiding the resonance, regardless of presence or absence of occurrence of the actual rotational speed abnormality. 
 
     
     
       4. The fuel cell system according to  claim 1 , wherein, when the abnormality of the rotational speed of the water pump is not avoided even when performing the S/C value averaging control, the control unit is programmed to presume that step-out of the water pump occurs, and stops the rotation of the water pump to stop the power generation operation of the fuel cell.